Outback inverter / load center wiring?

My plan to run the output of a single Outback VFX3648 inverter into a standard AC breaker panel just ran into trouble. The following is from Outback's installation guidelines:

"WARNING: To reduce the risk of fire, do not connect a single FX to both legs of a 120-240 VAC AC load center having multi wire (common neutral) branch circuits connected. Use two FX's wired in a series configuration..."

Huh? What possible fire risk? If the two hot sides of the panel are wired together to form a single hot, and there's no other AC source present (no grid tie, no generator input to this panel) I'm missing something.

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you sure are missing something as the 2 hots are not parallelable.WARNING!!!!!!!! across those 2 wires is 240vac that you would see flowing through the inverter thus smoking it minimumly and a fire possibly.

Hi, the key here is "multi-brach circuits" . Some installation uses 2 hot phases with a single common neutral return (10/3 for example) to supply 120V loads on each "branch". This is banged on the fact that the 2 hot phases are 180-deg out of phase and the combined current in the return neutral is the difference of the 120V loads currents on each hot phase "branch". Driving the 2 hot phases with the same phase would make the return current in the neutral to "add" and would exceed the current rating of the neutral wire and this is a fire risk since there is no circuit breaker in the neutral path.

If you run a separate neutral for each circuit, you should be all set.

However, consider whether you might want to just get a very large service panel, like a 200A one, with lots of slots, and only use one of the busbars instead of shorting both together. I'm not sure if there would be a kosher way of shorting both together, could be a little awkward. If you left one busbar free, and later wanted to add that second inverter, you could do so with minimal fuss. Also, let's say that in the distant future, you or someone else wanted to go grid-tied. After removing the old inverter, there's a very small, but nonzero chance that someone would overlook whatever was tying the two busbars together... I know, unlikely, but cowardice has its place.

Aha. Multi wire. Funny how you can read something, but not really read it.

would make the return current in the neutral to "add" and would exceed the current rating of the neutral wire and this is a fire risk since there is no circuit breaker in the neutral path.

If you run a separate neutral for each circuit, you should be all set.

Got it, can't share any neutrals, can't use "multiwire." I still haven't wired the house yet, so I just won't use multiwire. (Always wondered how they were able to "get away" with running just a single neutral for two hot wires, now it makes sense.)

Also, let's say that in the distant future, you or someone else wanted to go grid-tied. After removing the old inverter, there's a very small, but nonzero chance that someone would overlook whatever was tying the two busbars together...

There's no grid power here, nor is there likely to be, but it's a good point nonetheless: I'll make a big fat warning sign inside the panel!!